Simplex double acting water pump

[David MachinParticipant @davidmachin95465]

Has anyone made a Simplex double acting water pump exactly to drawing which works OK?

I ask this because I want to make a double acting water pump, and have examined the pump drawings for the Simplex Locomotive, designed by the late Martin Evans, and have difficulty in understanding how it works, particularly at one end of its stroke.

At the double ball end I can see its workings easily. But at the single ball end, after water has been delivered, there is no apparent passage for water to fill the enveloping volume as the piston moves towards the other end, when both balls will be closed to suction, as the delivery stroke at that end has started. As far as I can see, this will create a vacuum, perhaps only relieved when the piston arrives at the double ball end, when pressure of delivery falls there, and the balls will drop to allow a momentary flow to the vacuum at the single ball end. This would seem to require very rapid transfer of water at that point, and an inefficient system.

I would appreciate some help on this before I go mad, either making the pump in blind faith, or redesigning a better system!

Dave.

[David MachinParticipant @davidmachin95465]

difficulties in understanding how it works

[Simon CollierParticipant @simoncollier74340]

I have also been studying these lately. I read that the one for Super Simplex was a bit more developed, so that is the one I will (one day) build. It is a matter of staring at the diagrams until it sinks in. For Simplex, when the piston is moving forward, it is delivering water out via the rear clack you mentioned, but also filling the area behind the piston around the piston rod. When the piston is moving back again, it is sucking water into the front chamber via the bottom clack while the suction is closing the top clack; simultaneously, the water around the piston rod in the rear chamber is being delivered out via the back clack. I roughly calculated for the Super Simplex pump that the rear chamber delivers about half the volume of the main chamber. Hope that helps.

[julian atkinsParticipant @julianatkins58923]

the original design didnt work – it just moved water between one end and the other!

later in ME a revised design was published.

beware the fixing holes for the pump stretcher – they are a nightmare as require the wheels to be dropped plus disconnecting the conn rod to access same. this is a huge job (dont ask me how i know!)

so you want the revised design plus think about the pump stretcher bolts/screws. IMHO 2 injectors and no axle pump is the way to proceed.

cheers,

julian

[Stewart HartParticipant @stewarthart90345]

I've made a double acting pump for my simplex, to the plans published in ME as part of the Farlie article which leans a lot on the simplex design, they were early on in the build, I'll see if I can dig up the exact volume and page number, and post later.

Stew

[David MachinParticipant @davidmachin95465]

Many thanks for such a prompt response. I will look at the ME index to see if I can find the issue which will provide further enlightenment!

Dave.

[David MachinParticipant @davidmachin95465]

Julian,

I have looked at Super Simplex and also the Fairlie articles, and cannot see a redesign which suggests it would be any different.

In fact, the late Martin Evans is saying that he has done a redesign partly to reduce its water output! The other part of the redesign was to turn it round end for end, thus changing the drive end, i.e., from the sheave and eccentric. (This was to allow more room for other parts of the loco.)

So can you tell me where to look please?

Dave

[Stewart HartParticipant @stewarthart90345]

David

PM sent

Stew

[Derek DroverParticipant @derekdrover32802]

I'm not entirely sure why there was a modified design, but this one is supposedly less strain on the eccentric due to the reduction in water movement.

There is the issue with clearance from the weighshaft, so trying to put it in/out with the weighshaft isn't possible. If you refer to the below website, there are a number of hints:-

**LINK**

This includes a "notch" which allows the pump to be removed with everything in situ. It works.

Del

[michael mParticipant @michaelm]

Dave

I made my "Simplex" many years ago, in fact before the "Super Simplex" appeared. The pump was a novel design and though I didn't fully understand it as it seemed an odd method to get a double acting pump, I assumed the designer knew best and made it anyway. Shortly after the correspondence started to appear in the ME and the general consensus was that it simply didn't work properly. Eventually a redesign of a more traditional nature appeared so I decided to start again. I bought a new casting, from the original Reeves, and though I may be mistaken after so long I'm sure it was a casting to a new pattern. I put the original casting in my scrap box but with so many holes in it I've never been able to use it for anything. As currently my engine is without it's boiler I can see the casting does however look different. As.Julian said removal of the pump is awkward though with my boiler off it could be taken out without difficulty if the weight shaft was removed first. Clearly on a running engine one would only want to remove the boiler as a last resort. Another problem with the design was that as drawn the pump would clash with the weightshaft but being forewarned it's not too difficult to slightly redesign to avoid the problem. Later drawings may have been modified of course. As I said it was along while ago and we've had a house move since but at the weekend I'll have a look in the attic to see if I can find the modified drawing.

Michael

[Henry WoodParticipant @henrywood50588]

Hi David

The original design of ( Differential Double Acting Pump ) does work. I fitted this to my Simplex as per drawing and it has performed very adequately for the past 38 years. It is important to have a good gland seal on the rod. Based on this, I used the same type of pump but smaller on my Emma Victoria currently be serialized in M.E. This loco has been running for the past 8 years with he pump doing its duty very well.

Henry

[David MachinParticipant @davidmachin95465]

Many thanks for all your postings.

I would be grateful for any source of a redesign drawing, Michael, but presumably your pump works!! Also, I don’t know what you mean, Stew, when you say, ‘PM sent‘.

Dave.

[David MachinParticipant @davidmachin95465]

.

Thanks for your posting, Henry.

This is the first confirmation that the pump does work! Is the clearance of less than 1/8" between piston and end covers at each end of the stroke important? Pumps normally have little clearance here, but to get water to the single ball end on its suction stroke, (as I say in my first posting), this may be essential.

Dave.

[julian atkinsParticipant @julianatkins58923]

with the greatest respect to henry wood either his drawings were altered or he did in fact build the pump to the revised drawings and has forgotten!

give me awhile and i'll dig out the exact copy of ME where the revised design appeared. the original design caused an avalanche of letters to ME at the time so shouldnt be too difficult to find. the original is based on an E.T. Westbury design. edgar had died by the time the furore errupted in ME.

the SUPER SIMPLEX designed pump is quite ok . its the original SIMPLEX axlepump that is defective.

as michael m quite correctly states you either have to remove the boiler or drop the wheelsets to remove the pump once fitted.

as stated above i would dispense with same and fit 2 injectors.

cheers,

julian

[julian atkinsParticipant @julianatkins58923]

i should add that the original SIMPLEX axlepump will work after a fashion but it isnt truly double acting. it actually pumps a similar (but not more) amount of water as a single acting pump. this is perhaps why henry wood is under the impression his works ok.

cheers,

julian

[cParticipant @c]

The original 'Simplex' locomotive water pump is detailed on page 650 of Volume 133 of the ME (7 July 1967) and if built to the drawing, will pump.

The feed pump assembly is shown on page 651 and if built to these and other relevant drawings, the outlet clack housing will foul the weighshaft. A solution is to move the pump forward 1/8".

Again, if the locomotive is built to the drawings, it is possible to detach the pump from the frame stretcher and then remove it from below.

Does not 'double acting' mean delivering on both strokes; if it does then the 'Simplex' pump is double acting.

I regret not being able to find the 'avalanche of letters'. I would like to read them.

Chris.

[michael mParticipant @michaelm]

Dave

I've managed to locate the original drawing for the modified pump. It's MAP drawing LO935 sheet 6a. The original Simplex had 6 sheets of drawings only and the original pump was on sheet 2. The scantlings of the modified pump are somewhat larger than the original so there could be difficulties in using the original casting. As I said in my original posting I was sure that Reeves supplied a different casting for the new pump.

Re the original pump, Martin Evans states in his description that he used the "differential double acting pump" to give less jerky running at low speeds but concedes "I'm not too certain of the effective output of the pump". Hence the large bore of 5/8". hardly a very good basis for selling people drawings and expensive castings, but that's the world of model engineering.

The replacement pump has a bore of 7/16" diameter and again is double acting. I do remember, albeit somewhat vaguely, the correspondance on the topic, it certainly convinced me to change horses midstream and I've had no issues with the replacement pump. I can't recall who designed the replacement pump but would suggest that there must have been adequate concerns about the original for replacement drawings and castings to be provided.

Michael

[David MachinParticipant @davidmachin95465]

Many thanks to you all.

I would very much appreciate you finding, Julian, the relevant copy of ME in which the revised design appears. I will also try to get hold of the drawing sheet from ME, Michael, if Julian cannot find the ME, or runs out of precious time!

Dave.

[Henry WoodParticipant @henrywood50588]

Julian

With the greatest respect, the pump does work and is a differential double acting i.e. the amount of displacement on the forward stoke is equal to the volume of the rod, on the back stoke the displacement is equal to the annulus volume, i.e. the total displacement is the same as if the pump was a single acting.With the displacement being split, this helps to cut out jerky running with the by-pass valve fully closed. With regards to pump removal, when I was building my simplex, I had spotted early on that the pump / stay position was going to cause a problem with the weigh shaft and decided to move it 3/8" i.e. a pitch of the fixing screws.

Henry

[David MachinParticipant @davidmachin95465]

Once again, many thanks to you all. I have found the revised design.

First, I must apologize to you, Julian, for asking you to look out the relevant ME. I have an ME index book, and could do it myself, which I've just done!

I have found the copy of the relevant ME, and the revised design, which has, significantly, 4 x 1/4 inch balls, and I can now see that it will work. If anyone wants to know, it is an article by Martin Evans on Page 273, Vol 146, March 7, 1980. There are numerous follow up letters the same year in postbag about this.

My very grateful thanks to you all, since in the end, you led me to the improved design, which I didn't know existed. Shows how more thoroughly you read – and remember – the articles than me! My excuse is that I was working then – but then, I would expect, so were you!

Dave.

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